Recently, I was called out for abandoning Segment Triangulation.  Let me set the record straight. I like, and use, both Clustering and Triangulation – virtually every day! Each one has some unique strengths and some drawbacks. A (very) short review….

Triangulation. When I started Segmentology, in 2015, I was the Johnny Appleseed of Segment Triangulation. I don’t claim to have invented it, but I was definitely a fan, and, I think, took it to new levels. It has been called the “Gold Standard” in genetic genealogy. Your DNA is composed of specific DNA segments from specific Ancestors – Triangulation helps you to determine these segments, group your Matches by shared segments (and therefore ancestral lines), and develop (or “paint”) a Chromosome Map of segments. However, the critical step of determining the ancestral line is often hard (at least for me) because the companies providing segment data, in general, don’t have any/many good Trees.

Clustering. In late 2018, auto-Clustering was introduced, and we could easily get many Clusters depending on the range of cMs we used. With this tool, you could determine these families of cousins, group your Matches by shared Matches, and try to determine the Common Ancestor. This was a tool we could use with AncestryDNA (either auto- or manual Clustering), where there tended to be many more Trees and genealogy tools. It worked for me… However, at AncestryDNA we cannot get the segment data to tie Matches to DNA segments.

By 2020 I had finished my Triangulation and had 372 Triangulated Group (TG) Segments. I was growing frustrated because I wasn’t getting very far finding Common Ancestors. On the other hand, I was finding a lot of Clusters with pretty solid Common Ancestors. So, I shifted my focus and have mainly been using Clusters, ever since. I still look for close Matches with larger segments for Triangulation. But my focus is on confirming more distant Ancestors and working on Brick Walls – mostly with Shared Match Clustering.

Bottom Lines:

1. Comprehensive Triangulation is a lot of hard work; but it can be a good tool for specific segments that appear to come from/through a Brick Wall.

2. Clustering is somewhat easier and focuses more directly on the genealogy. I think it’s more fun; and a better tool for many hobby genealogists. A spreadsheet is not required (but it is helpful to track everything).

3. Again: I use both, every day!

[22DL] Segment-ology: Clustering vs Triangulation; by Jim Bartlett 20260407

In genetic genealogy, DNA is a tool. It helps us, in many different ways, to determine Ancestors and confirm cousins. My point in this blogpost, is that we don’t need to know precisely how we are related to each cousin – a calculated guess is fine. In fact, I encourage it.

Here is an example. I have determined that XYZ is a 7C. This is based on genealogy. We share my Ancestor couple METZGER/KEIFFER (aka Ahnentafel 352). This Ancestor couple’s full names, dates, places, life story are not important to Segmentology. Match XYZ happens to share 15cM, also not too important, but well within Shared cM range. XYZ is on my Paternal side, as is our MRCA. XYZ and I have over 30 other Matches on our Shared Match list – the top 20 Shared Matches share over 100cM with XYZ. I can tell you that this will show up as a strong, solid Cluster. You get the picture; this is pretty solid…

So now I notice on my Shared Match list with XYZ that, per ProTools, ABC is a 1C to XYZ, sharing 852cM. ABC has NO Tree. However, ABC has a long Shared Match list with over 30 Matches who are known cousins to me through Ahnentafel 352. #A0352P is the first thing in many of my Shared Match Notes, which is all I need to know…

There is no Tree for ABC, but as a 1C to XYZ, I don’t need a Tree. I know XYZ’s grandparents, must also be ABC’s grandparents for them to be 1C. So, I confidently add ABC to my Common Ancestor spreadsheet and copy the line of descent I already have for XYZ, and change ABC’s parent to UNK. Done!

I’ve now added ABC to the Shared Match spreadsheet, and can enter a Note for ABC which starts #A0352P. Which Note is now visible to all other Shared Match lists (and Clusters) that include Match ABC. This helps me find even more Matches to evaluate and add.

Emboldened by this logic, I am sure I can also add a proposed 2C to my spreadsheet (with  UNK for both parent and grandparent). This will “tuck” many more Matches into my spreadsheet of known cousins, even though I don’t know their parents or grandparents. And those Matches will often highlight other Matches who can be added. For A0352P, I now have 151 confirmed Matches!

Note: It’s important that these potential additional Matches be vetted (as above). They should also be part of an appropriate Cluster of Shared Matches. Even the parent of a known Match can be on the wrong side. That is to say, for instance, my line from XYZ goes through her mother – so her tested father could well show up as a close match to XYZ, and to me, but his path to a CA would be different (ie NOT through his wife to A0352P!).

In conclusion, there are two options:

1. Leave this “Match with no Tree” out of my Tree – disavow them as a cousin because *I* don’t know their parent’s name.

2. Accept this Match as a 7C to me; just as much as I accepted XYZ as my 7C.

To me, as a lifelong genealogist, I’d choose Option 2 in a heartbeat. I’d hug this new Match just as strongly at a family reunion. I’d probably ask their parents’ names… But the rest of their line would already be in my spreadsheet. The UNK parent/grandparent wouldn’t make any difference. And, that Match will now help me document other Matches!

AND, often this new cousin Match doesn’t know much of their Ancestry – be a helpful genealogist, and send them a message about the ancestry you are sure they have… Add their line to your Tree, and ask if they’d like you to add names in place of the UNKs!

This is also a plug for the Common Ancestor spreadsheet – a valuable tool for recording found cousins, and for easily seeing how other Matches fit in. Hard work, but it sure highlights strong branches of my family Tree (as well a weak branches).

[35BCa] Segment-ology: A Calculated Guess Is Great; by Jim Bartlett 20260403